<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
    <style>
      div.box {
        color: red;
      }

      div .box {
        background-color: green;
      }
    </style>
  </head>
  <body>
    <div class="box">这是第一个div元素</div>
    <div>
      <p class="box">这是第一个p元素</p>
    </div>
  </body>
</html>
